The standard method used to load and off-load passengers onto jet aircraft passenger liners is through the use of a Passenger Boarding Bridge (PBB). A Passenger Boarding Bridge is a moveable walkway that attaches to the airport terminal building at one end and at the other end is capable of being driven to join the aircraft door. This provides a continuous walkway from the aircraft to the terminal. Typically, Passenger Boarding Bridges, in addition to providing a smooth floor surface have side walls and a roof to protect passengers from the elements. In addition to providing a convenient walkway for passengers, the Passenger Boarding Bridge is also used to mount pieces of equipment that service the aircraft docked at the Passenger Boarding Bridge.
The subject of this Patent Application is for one such piece of equipment. It is a common practice to install a 400 Hertz power supply to the underside of a PBB to provide electrical service to the aircraft while its engines are shut off. The power transmission cord is a large heavy extension cord weighing as much as 250 pounds. When this cord is left lying on the tarmac, it is easy for the cord to be run over and damaged as the PBB is driven up to or hacked away from the aircraft. Therefore, it is common practice to locate a winch on the PBB such as at the roof level of the PBB, on the side closest to the aircraft, to hoist the cable off the ground while not in use, thereby keeping it out of harm's way.
All such cable winches use a wire rope wound around a drum attached to a motor to raise and lower cable clamps attached to the 400 Hertz power cable. All such winches use an upper limit switch consisting of a slotted cable guide on a hinge that when a Fob, larger in diameter than the width of the slot in the cable guide comes in contact with the cable guide, it is then lifted and strikes a mechanical switch, turning off the motor.
The problem with such an upper limit switch device is that if the cable is not directly under the winch, the cable, owing to its divergence from vertical, moves the upper limit cable guide up, thereby shutting off the winch before the cable has been taken up. Because of this inherent problem, the winch operator must gather the wire rope and the 400 Hz power cord directly under the winch in order to hoist it up. The present invention described hereinafter allows the winch to operate regardless of the angle of the wire rope to the winch. There is never a need for the operator to gather the 200 pound plus cable under the winch in order to raise it.
Additionally, with other hoists, it is possible for the operator to completely unroll the wire rope from the drum. In that case, the wire rope can be easily rewound the wrong way on the drum, so that when the down button is pressed, the rope actually goes up. Subsequently the motor can be overloaded to the extent that a fuse would be blown. Some hoists employ a switch connected to a lever that trips if the cable starts in the wrong direction on the drum. However mechanical switches and levers are difficult to adjust, add extra expense and complicate the design. The present invention precludes the possibility of the cable winding the wrong direction on the drum without the use of a separate switch and lever.
Additionally, it is customary to include another separate switch that is activated by the position of the cable guide to disable the bridges ability to be driven until the cable is all the way up in its home position. The present invention incorporates that requirement in the wire rope guide and therefore eliminates the need for a separate switch.
An inherent problem existing with all prior art hoist systems used on PBB's is excessive wire rope tensioning. In order to suspend a 250 pound static load aloft on a drum while not in use requires the addition of a mechanical break on the electric winch motor. In all other cable hoists, as soon as the upper limit switch on the wire rope guide goes open, the motor break is employed. The break is deployed before the motor can ramp down. Therefore the motor comes to a jarring halt and the full torque load is placed on the wire rope guide and the wire rope, not to mention the drive bearings. This needless torque load which is many times that of the weight the hoist is designed to lift shortens the life of the wire rope and the motor.